The present invention relates to plastic injection molds and, more particularly, to devices for separating the molded product from the mold feedline, or runner.
Various types of plastic injection molds are utilized in the industry. In general, the injection molding process includes preheating, plasticizing, and shaping of the molded product within the same tool machine. In the typical injection molding process, granules of a thermal plastic material, having high fluidity, are introduced through a hopper into a cylinder, in which they are heated, e.g., by means of a heating jacket, to above their softening point. The moving piston then plasticizes the material and forces it through a nozzle into the mold.
The molding machine typically comprises separable mold portions or platants, one being stationary, and the other being moveable. The plastic material typically enters the mold through a sprue and runner system, and then flows along the interface of the stationary and moveable mold portions. As the moveable portion of the mold retracts the molded product and the plastic feedline, known as a runner, remain attached to the surface of the moveable mold portion and retract with the moveable mold portion, thus separating the runner and molded product from the feedline to the mold port. Reciprocating ejector pins mounted in the moveable mold portion then advance toward the mold surface to separate mold product and the runner from the mold surface. Upon separation from the mold surface, the runner and molded product fall into a catch basin.
For some mold products, such as parts for model airplanes, and the like, the mold runner may remain attached to the part. However, for many mold products, it is not acceptable for the product to remain connected to the runner, or even for there to be any surface distortions resulting from the separation of the product and the runner.
Separation of the product and the runner may be effected by the utilization of certain techniques for gating the plastic into the mold. In general, a mold gate serves as a door between the runner and the part, and acts as a control valve in filling out the part. Customers for high quality, expensive plastic parts typically require that runner and gate remnants be kept within close specifications or the plastic parts will be rejected.
The most common type of gating is known as edge gating wherein the runner connects to the part normal to an end edge portion of the part. Edge gating typically results in surface distortions, requiring an operator to manually trim those distortions from the part. Other gating techniques, such as submarine gating, differ from edge gating in that the runner connects to the part away from the end of the part. Such alternative gating techniques permit the part to be automatically separated from the runner and trimmed upon separation of the mold. Hot tipped manifold gating is another technique which automatically separates a part from the runner.
Even though techniques such as submarine gating will permit the part and runner to be clearly separated upon separation of the mold, both the part and runner remain attached to the surface of the moveable mold portion until the ejector pins axially reciprocate within the moveable mold portion, causing both the part and runner to be discharged from the face of the moveable mold portion into the catch basin. Contemporary systems typically eject the part and runner at the same time onto a common catch basin or a common conveyer system. The conveyer system then carries the runner and molded parts to operators who then sort the parts and runners by hand, or operate a parts/runner separator device operatively connected to the conveyer system.
The employment of operators to manually sort runners from parts, or the utilization of various automatic sorting systems, add substantial costs to the price of producing the plastic product. Moreover, neither the manual system nor the automatic system for sorting are without error, and both may be difficult to implement with particular molds or applications. Further problems in sorting runners from parts my arise from the need to prevent contamination of plastic parts used, for example, in medical applications.
The present invention provides an apparatus and technique for sorting molded products from the mold runners within the mold itself. The invention may be incorporated into new molds, using standard mold base components, or it can be added to existing molds. The invention avoids the need for parts to be separated on parts/runners conveyer systems, therefore reducing labor costs and avoiding any need for complicated, expensive robotics, or other sorting machinery.